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Old 02-19-2015, 11:55 PM   #51
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which one?
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Old 02-20-2015, 02:50 PM   #52
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Originally Posted by ol trunt View Post
which one?
If I have time tonight, I will draw you a picture.

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Old 02-20-2015, 04:11 PM   #53
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If this ceramic impregnated paint was not white, it would never sell. The only results people are seeing is due to the white color of the paint.
Well.... there is NO question that color is critical, as you say. One of my previous projects was a Cozy MKIV, a fiberglass airplane. Because the foam and epoxies can't be allowed to overheat, and the planes are regularly outside in the sun (duh...) they are super-specific about what colors you're allowed to use, and where. There's even a chart:



This chart is for fiberglass-over-foam and the "ambient air temp" is calculated to allow for some amount of heat to be safely dissipated - it's irrelevant for skoolies, so ignore it. The curves are mostly parallel - you can pick any vertical line to follow and the point would still be the same.

Notice that white is even better than naked aluminum?

That said, I'm not sure what the ceramic additive would do, but those micro-balloons somebody mentioned are also used in Cozy construction, in this case not as an insulator but as a lightener for areas that need filler (you don't slap Bondo on a dent in a fiberglass airplane - "micro" weighs a fraction as much). But there is absolutely no doubt that they DO provide some insulation. It's very easy to prove. Epoxy produces heat as it cures - and heat speeds its reaction. A lot. A pot of 40-min set-time epoxy can "kick off" literally in 5 minutes once you pack it full of micro. The micro insulates the mixture and stops the heat from radiating out from the center, and heat builds up there really quickly.

The problem with either of these is that we're talking super-thin coatings. I wouldn't count on a layer of paint to stop heat TRANSFER. You just want the very outside layer to minimize heat ABSORPTION.

Personally, I agree with what (I think) nat_ster is saying: white paint and spray foam are probably the best combo. They're what I plan to use, anyway.

Side question: what are you guys doing to cut thermal "bridges"? Spray foam is fine between the ribs, but I have to attach walls TO those ribs - what's the best way to deal with those areas?
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Old 02-20-2015, 09:04 PM   #54
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Cool chart, thanks for sharing. I'm going to have me a closer look at that.

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Originally Posted by taskswap View Post
Side question: what are you guys doing to cut thermal "bridges"? Spray foam is fine between the ribs, but I have to attach walls TO those ribs - what's the best way to deal with those areas?
I'm using what I call wood strapping.
I run strips of wood 3.5 inches wide by 1.5 thick across the upright support ribs, running horizontal.
I spray foam the 3.25 inch space behind the strapping till it's flush with the surface of the strapping.
Then I glue 2 inch thick sheets of rigid Styrofoam to the surface of the spray foam and strapping.
Everything you mount on the inside screws into those ribs every 16 inches from the floor to the ceiling.

This provides a true thermal brake.

Now here is a variation of this method.
Do the strapping the same, but glue the rigid Styrofoam to the surface of the strapping before spray foaming the space behind.
Now use pour foam, poured in batches from the top.
This bonds the foam to the inside surface of the rigid Styrofoam sheet far better than any adhesive can.
This method also skips the step where you have to shave all the over spray of the foam.
Over spray is the spray foam that expands beyond the surface of the strapping. Unless shaved, we cant glue the rigid Styrofoam in place.
For the fellow skoolies that have used spray foam them selves, they know this is a massive amount of work, And tremendously messy.



A hybrid system. We would skip the plastic, and substitute the plywood for the rigid Styrofoam, and back it with the plywood till done curing.



Skip to 5:00 to see a fast way of cutting.



Nat
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Old 02-20-2015, 09:42 PM   #55
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Now here is a variation of this method.
Do the strapping the same, but glue the rigid Styrofoam to the surface of the strapping before spray foaming the space behind.
Now use pour foam, poured in batches from the top.
This bonds the foam to the inside surface of the rigid Styrofoam sheet far better than any adhesive can.
Cool, thanks for all the thoughts. This option here is basically what I had planned - I'm kind of a fan of pour foam. I tried one of those DIY spray foam kits once and was a total spaz with it. My thicknesses were all over the place, and I know exactly what you mean about what a pain it is to get a good final surface. Pour foam is a guaranteed 100% seal, everywhere.

I figured I would use thick plywood screwed to the vertical struts as a mold and plastic sheeting as a release - the pour foam I've used in the past was pretty happy letting go of that. It's just a pain to do overhead, so I guess I've been still poking around looking for an "elegant" solution.
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Old 02-20-2015, 09:49 PM   #56
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I used 1x2 pine that we called "furring strips" for thermal breaks. The ceiling was a different matter all together.

Look, just do what you want. If you want to insulate the exterior, then go for it. It is YOUR bus. You may want to do a smaller Test to see how hard it is to shape the foam and all.
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Old 02-20-2015, 10:26 PM   #57
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Hey, great to hear there's another homebuilder on here! I've got a Q2 kit I'm currently working on.

And that's why I had micro handy to pour into my paint for the roof. Somewhere along the way I had realized that the ceramic stuff for insulating was the same stuff we used as filler, just advertized differently.

There's a thread somewhere on here where someone used sawdust as a filler and it actually worked a little better than the "ceramic" stuff.

If you're willing to do the work it seems to me that the spray in stuff is the way to go.
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Old 02-20-2015, 11:09 PM   #58
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You know, there's a lot of talk about walls and ceilings but not as much about floors. I'm a newbie here - mostly planning for a bus I'm about to buy and convert. I'm looking at a Thomas that has big wheel-wells so I kind of figure it's going to make more sense to insulate inside - that way I can build up the floor so they're not in the way as much. But has anybody done much with the outside? It seems like a good area to get some extra R-value...
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Old 02-21-2015, 02:23 AM   #59
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Well, I took the time to read the whole thread...

So, we know we can raise the roof fairly easily. And if the roof is raised enough we can add insulation to the floor, put in radiant heat easily, plumbing in the floor, etc. and still have plenty of vertical space. However, expanding side to side is much more of an endeavor. Slide outs are an option but seems like more work than raising the roof.

When I owned a model 5 Eagle bus it was easy to dream about the 6" wider model 15. And on the Eagle forum there have been people that welded up the frame of a model 5 to give it more width. Those that went from the 5 to the 15 said that the extra space was nice.

So adding foam to the outside wall and skinning it over might be a worthwhile endevour. Easiest and cheapest seems to me to be the 4x8 foam sheets. Get some cheap fiberglass from Thayercraft to epoxy for the skin or some thin gauge sheeting. Seems like puncture resistance would be decent. Framing out the windows would be easy. The wheel wells would be more of a challenge but not too bad. Fairing in the front and back would take some thinking but seems easy. And the rear duallys on the bus stick out a little so having 1 or 2" wider walls shouldn't make it look like those RV's where the body is too fat for the chassis.

I don't know anybody that's done it but hey, sounds like a possibility to me!
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Old 02-21-2015, 08:22 AM   #60
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So adding foam to the outside wall and skinning it over might be a worthwhile endevour. Easiest and cheapest seems to me to be the 4x8 foam sheets. Get some cheap fiberglass from Thayercraft to epoxy for the skin or some thin gauge sheeting. Seems like puncture resistance would be decent. Framing out the windows would be easy. The wheel wells would be more of a challenge but not too bad. Fairing in the front and back would take some thinking but seems easy. And the rear duallys on the bus stick out a little so having 1 or 2" wider walls shouldn't make it look like those RV's where the body is too fat for the chassis.
Finally, an area where I actually KNOW something. You can totally do that, but be prepared for the job to get bigger and more expensive as you go. I'm starting to get the sense from other posts and responses that being negative about ideas is frowned on here, so hopefully I'm not about to piss somebody off...

The thing is, this is a HUGE surface area to cover - the equivalent of, say, a handful of DIY boat projects. Fiberglassing a large surface by hand is a lot of work because you don't just roll it out and walk away - you have to either vacuum-bag it or manually "stipple" all the air bubbles out, and it's a slow process. You can't make up too much epoxy at a time, either or it "kicks off" (overheats and basically cooks itself). There are techniques to address all these points, but it's a lot of work.

You also need to attach that foam to the inside in a way that won't detach in the heat, or due to differing expansion/contraction factors. You'll need flox for structural corners and areas, and micro to "prep" the outside (because fiberglass laid right over foam doesn't "stick" - you need to fill the holes in the cells first). Then you need MORE micro for the outside to prep for paint, and many hours of sanding.

If you were going to insulate the outside I'd personally stick with a metal skin. It eliminates a lot of those issues, you can just rivet it all together, and it's already basically paint-ready if you don't ding it while you work.
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